The overall prevalence of dry eyes was found to be 14.4% in a cohort aged 48 to 91 years (Moss et al., 2000, which publication is hereby incorporated in its entirety by reference). It has also been estimated that one in four patients consulting ophthalmologists complain of dry eyes and up to 20% of adults aged 45 years and older experience dry eye symptoms (Brewitt et al., 2001; which publication is hereby incorporated in its entirety by reference).
Contact lenses provide a valuable option to the vision impaired. Although contact lenses have been much improved, irritation is still a common problem and wearers often experience symptoms of xerophthalmia due to moisture loss from the contact lenses (Bowling, 2007, which publication is hereby incorporated in its entirety by reference.)
Dry eye disease and the symptoms thereof are vastly different from allergic conjunctivitis and similar allergic, inflammatory or allergic/inflammatory diseases. The symptoms for dry eye disease include dryness, burning, sandy-gritty eye irritation, foreign-body sensation, photophobia (Keratoconjunctivitis sicca. Wikipedia, October 2008; which publication is hereby incorporated in its entirety by reference.) The most common symptoms for allergic conjunctivitis are red eyes and itching, which is associated with allergies and are related to release of histamine and other mediators (Allergic conjunctivitis. Eye facts. Univ. of Illinois; which publication is hereby incorporated in its entirety by reference.)
Ketotifen molecules can be demethylated in the liver, but not in the eye, to form norketotifen, which is therefore a hepatic metabolite of ketotifen. In the USA, ketotifen has received regulatory approval for the treatment of ocular allergies, and is marketed under the name Zaditen®, Novartis.
Pharmacological effects of norketotifen and are shown in Examples 1, 2, 3 and 4 of this document.

Ketotifen is available commercially from Sigma-Aldrich (Internet: Sigma-Aldrich.com/order). Norketotifen is not available commercially and was custom-made according to the method of Waidvogel et al. 1976, which publication is hereby incorporated in its entirety by reference.